Indictment leaves room to add defendants to a case that could reach Mayor Rahm Emanuel’s office.

Three officers who helped cover up the circumstances surrounding the police killing of teenager Laquan McDonald in 2014 will face criminal conspiracy charges, a special prosecutor in Illinois announced Tuesday.

McDonald’s killer, Officer Jason Van Dyke, still awaits trial on homicide charges in the case. Initially, Van Dyke and other officers at the scene reported that the knife-wielding teen had lunged at officers, supposedly prompting Van Dyke to shoot him 16 times.

Similar records pursuits revealed emails indicating that Emanuel’s staff had seen the footage within months of the killing, but did not make clear whether Emanuel himself had viewed the footage or been told that it showed sworn officers of the Chicago Police Department were engaged in a cover-up. When staff first learned of the tapes, the emails show, Emanuel was just a few months away from re-election.

“It was the object of the conspiracy to conceal the true facts of the events surrounding the killing of Laquan McDonald,” Tuesday’s indictment says. “[T]he co-conspirators lied about what occurred and mischaracterized the video recordings so that independent criminal investigators would not know the truth about the Laquan McDonald killing and the public would not see the video recordings of the events.”

Detective David March and Officers Joseph Walsh and Thomas Gaffney will now face charges for the cover-up. The indictment also notes that “others known and unknown” to the grand jury aided the conspiracy, implying that the case could expand.

After the forced release of the videos proving Van Dyke had shot McDonald while he stood in the middle of the street, armed with a knife but not menacing any officer, Emanuel fired then-Police Superintendent Garry McCarthy. Voters also eventually fired former Cook County State’s Attorney Anita Alvarez, who declined to prosecute Van Dyke or any of the alleged cover-up conspirators throughout the year-plus legal battle over the shooting tapes. The department has sought to fire Van Dyke and four other officers involved, but the officers have contested the discipline.

Van Dyke’s criminal case, like all such cases, will be difficult for prosecutors to win. Juries are instructed to give immense deference to a police officer’s judgment when deciding if their on-duty actions constituted a criminal act. Four police officer trials in the past six weeks in high-profile on-duty killings have failed to return a single guilty verdict.

But the bar for the parallel conspiracy case is different and lower. Prosecutors must prove that March, Walsh, Gaffney, and any other people that could be later added to the indictment knowingly and intentionally falsified the record to stymie investigations into Van Dyke’s actions. They will not, however, be bound by the “reasonable officer” standard that governs police killings trials.

Trials are only one dramatic way of seeking police accountability. Another involves court-enforced agreements between federal civil rights lawyers and local decision-makers. The previous administration had sought such a deal with Chicago over what federal investigators deemed an abusive “cowboy” culture in the city’s police force.